Simultaneous Dual Isotope Research Articles

Prediction of myocardial viability in chronic phase in patients with acute myocardial infarction by simultaneous dual-isotope imaging with 99mTc-sestamibi/123I-BMIPP SPECT using CZT camera system

Abstract Objectives The objective of this study was to determine the optimal cut-off value of % uptake of simultaneous dual-isotope (99mTc-sestamibi/123I-BMIPP) SPECT in patients with acute myocardial infarction (AMI) for prediction of myocardial viability in chronic phase. Methods We evaluated 30 consecutive patients with AMI who had undergone both dual-SPECT in acute phase and stress myocardial SPECT using 99mTc-tracers in chronic phase by Discovery NM530c. Regional % uptake with a 17-segment model was obtained using QPS software. The presence of myocardial viability was defined when regional % uptake ≥50% in 99mTc SPECT at rest in chronic phase was observed. Receiver operating characteristic (ROC) curves were analyzed to determine the optimal cutoff values of regional % uptake in both left anterior descending artery (LAD) territory and non-LAD coronary territory in acute phase to predict the myocardial viability in chronic phase. Results The cutoff values for prediction of viable myocardium were %uptake ≥47% for 99mTc-sestamibi, %uptake ≥31% for 123I-BMIPP in acute phase in LAD territory and %uptake ≥52% for 99mTc-sestamibi, %uptake ≥48% for 123I-BMIPP in non-LAD territory. The respective sensitivities, specificities and the area under the ROC curve (AUC) values in the prediction of myocardial viability were 92%, 92% and 0.94 with 99mTc-sestamibi, 90%, 85%, 0.92 with 123I-BMIPP in LAD territory, and 81%, 93% and 0.92 with 99mTc-sestamibi, 81%, 90%, 0.92 with 123I-BMIPP in non-LAD territory. There were no significant differences in AUC values between 99mTc-sestamibi and 123I-BMIPP in both LAD territory and non-LAD coronary territory. Conclusions In the simultaneous 99mTc-sestamibi/123I-BMIPP dual-isotope imaging in patients with AMI, these results suggest that not only 99mTc-sestamibi SPECT, but also 123I-BMIPP SPECT may be possible to predict the presence of myocardial viability in chronic phase. But it should be noted that the optimal cutoff values of regional % uptake in acute phase to predict the myocardial viability may differ for LAD territory and non-LAD coronary territory. Funding Acknowledgement Type of funding source: None

Prediction of the improvement of left ventricular wall motion after acute myocardial infarction by simultaneous dual-isotope imaging with 99mTc-sestamibi/123I-BMIPP using cadmium-zinc-telluride SPECT

Abstract Background/Introduction Although both the presence of 99mTc-sestamibi/123I-BMIPP mismatch and the reverse redistribution of 99mTc-sestamibi in patients with acute myocardial infarction (AMI) are known to significant markers for predicting the improvement of left ventricular (LV) wall motion in the infarcted territory in chronic phase, few studies evaluated them by simultaneous dual-isotope (99mTc-sestamibi/123I-BMIPP) imaging using cadmium-zinc-telluride (CZT) SPECT system. Purpose The purpose of this study was to evaluate whether the presence of 99mTc-sestamibi/123I-BMIPP mismatch or the reverse redistribution of 99mTc-sestamibi make better prediction of the improvement of LV wall motion in the infarcted territory. Methods We evaluated 30 consecutive patients with AMI who had undergone both dual-isotope (99mTc-sestamibi/123I-BMIPP) SPECT in acute phase and stress myocardial SPECT using 99mTc-tracers in chronic phase by Discovery NM530c. Both 99mTc-sestamibi/123I-BMIPP mismatch and reverse redistribution of 99mTc-sestamibi were determined using traditional definition. The improvement of LV wall motion in the infarcted territory from acute phase to chronic phase was assessed using QGS. Results Of 30 patients, the improvement of LV wall motion in the infarcted territory from acute phase to chronic phase was found in 20 patients. Both the presence of 99mTc-sestamibi/123I-BMIPP mismatch and reverse redistribution of 99mTc-sestamibi were significantly linked to predict the improvement of LV wall motion (p=0.0001, p=0.011, respectively). The respective sensitivities, specificities and accuracies in the prediction of the improvement of LV wall motion in the infarcted territory were 90%, 90% and 90% with 99mTc-sestamibi/123I-BMIPP mismatch, and 60%, 90%, 70% with reverse redistribution of 99mTc-sestamibi. Conclusions In the simultaneous 99mTc-sestamibi/123I-BMIPP dual-isotope imaging using CZT SPECT system, both the presence of 99mTc-sestamibi/123I-BMIPP mismatch and the reverse redistribution of 99mTc-sestamibi in acute phase are useful for predicting the improvement of LV wall motion in chronic phase, but the presence of 99mTc-sestamibi/123I-BMIPP mismatch is superior to the reverse redistribution of 99mTc-sestamibi for it. Funding Acknowledgement Type of funding source: None

Simultaneous dual isotope (i123/tc99m) cardiac spect by using CZT camera

La scintigrafia miocardica con l’utilizzo del sestamibi marcato con Tecnezio 99m e metaiodobenzilguanidina (MIBG) marcata con Iodio123, ha lo scopo di mettere in correlazione lo studio della perfusione cardiaca, ottenuta dalla distribuzione del 99mTc, e la valutazione dell'innervazione cardiaca-simpatica che può essere direttamente studiata con un analogo della noradrenalina radiomarcato con Iodio 123 che riflette l'integrità neuronale visualizzando il recupero e l’ uptake nei terminali simpatici cardiaci. Tale studio fatto utilizzando gamma camere di nuova generazione, che adoperano rivelatori composti da cristalli di Tellurio di Cadmio Zincato(CZT) utilizzate esclusivamente per la valutazione miocardica, ha dimostrato come la perfusione combinata all’imaging d’ innervazione simpatica, consente la valutazione della discrepanza di innervazione-perfusione.

Simultaneous dual isotope (i123/tc99m) cardiac spect by using CZT camera

La scintigrafia miocardica con l’utilizzo del sestamibi marcato con Tecnezio 99m e metaiodobenzilguanidina (MIBG) marcata con Iodio123, ha lo scopo di mettere in correlazione lo studio della perfusionecardiaca, ottenuta dalla distribuzione del 99mTc, e la valutazione dell’innervazione cardiaca-simpaticache può essere direttamente studiata con un analogo della noradrenalina radiomarcato con Iodio 123che riflette l’integrità neuronale visualizzando il recupero e l’ uptake nei terminali simpatici cardiaci.Tale studio fatto utilizzando gamma camere di nuova generazione, che adoperano rivelatori compostida cristalli di Tellurio di Cadmio Zincato(CZT) utilizzate esclusivamente per la valutazione miocardica,ha dimostrato come la perfusione combinata all’imaging d’ innervazione simpatica, consente la valutazione della discrepanza di innervazione-perfusione.

Comparative Cardiac Phantom Study Using Tc-99m/I-123 and Tl-201/I-123 Tracers with Cadmium-Zinc-Telluride Detector-Based Single-Photon Emission Computed Tomography.

A recently introduced single-photon emission computed tomography (SPECT), based on cadmium-zinc-telluride (CZT) detectors (D-SPECT), supports high energy resolution for cardiac imaging. Importantly, the high energy resolution may allow simultaneous dual-isotope (SDI) imaging (e.g., using Tc-99m and I-123). We quantitatively evaluated Tc-99m/I-123 SDI imaging by D-SPECT in comparison with conventional T1-201/I-123. Energy resolution was measured as a percentage of the full width at half maximum (FWHM) for Tc-99m, I-123, and Tl-201. The impact of cross-talk and reconstructed image contrast were quantified by measuring the contrast-to-noise ratio (CNR), and the transmural defect contrast in the left ventricle wall (C TD) induced by a difference in energy, for combinations of Tc-99m/I-123 or Tl-201/I-123, using an RH-2 cardiac phantom. Corresponding measurement was also carried out in Anger SPECT (A-SPECT). The energy resolution of the D-SPECT system was 5.4%/5.1% for Tc-99m/I-123 and 5.4%/5.3% for Tl-201/I-123, which was approximately two times higher than the A-SPECT. No notable difference was confirmed in the CNRs of the two systems, but T1-201/I-123 showed overall higher value than Tc-99m/I-123. Compared to A-SPECT, C TD of D-SPECT significantly increased with both Tc-99m/I-123 and T1-201/I-123 (p< 0.05). In DSPECT, the combination of Tc-99m/I-123 had a slightly better C TD than T1-201/I-123. In addition, C TD of Tc-99m/I-123 was improved with scatter correction at both nuclides (p< 0.05), but in Tl-201/I-123, no significant improvement was confirmed in I-123 (p> 0.05). D-SPECT was considered to be capable of performing high-quality SDI imaging using Tc-99m/I-123.

Feasibility of simultaneous dual isotope acquisition for myocardial perfusion imaging with a cadmium zinc telluride camera

BackgroundWe studied the impact of technetium-99m (99mTc) in the thallium-201 (201Tl) energy window (70 keV) to determine if CZT cardiac cameras allow us to perform simultaneous dual-isotope acquisition for myocardial perfusion imaging. MethodsWe included 117 consecutive patients. We injected 0.7 MBq/kg of 201Tl at stress, performed the first scan (image T1), then injected at rest 2 MBq/kg of 99mTc-tetrofosmin and immediately acquired a second scan with reconstruction in the energy window of thallium (image T2). A corrected thallium image was created by the subtraction of 99mTc downscattered photons (image TS). We compared spectra, image quality, and semiquantitative scores on T1, T2, and TS images. ResultsThough T2 images were of worse quality, TS images were of equal quality compared to T1 images in most cases. Scores show an underestimation of abnormalities in 20% of patients on T2 images and in 10% on TS images. ConclusionsDespite the improved energy resolution of CZT cameras, downscatter of technetium in the 201Tl window leads to an underestimation of the pathological territory in 10% to 20% of cases. It does not allow us to use simultaneous dual-isotope acquisition in clinical practice without additional tools for scatter correction.

First assessment of simultaneous dual isotope (123I/99mTc) cardiac SPECT on two different CZT cameras: A phantom study

BackgroundWe studied the impact of simultaneous dual-isotope acquisition on 123I/99mTc mismatch assessment using two CZT cameras (DNM 530c, GE Healthcare and DSPECT, Biosensors International). MethodsWe used an anthropomorphic torso phantom (respectively filled with a solution of 123I alone, 99mTc alone, and a mixture of 123I and 99mTc) and its cardiac insert with two defects mimicking two matched and mismatched defects. Mismatch extent and reconstructed image contrast were evaluated. ResultsThe acquisition mode (single vs dual) significantly impacted (i) 99mTc (but not 123I) reconstructed segmental activities using both camera (P < .001), and (ii) image contrast (using 123I and DNM 530c, P < .0001; and using both 123I and 99mTc with DSPECT, P < .0001). However, the defect and mismatch size were not impacted by the type of acquisition. With both DNM 530c and DSPECT, Lin’s concordance correlation coefficient and Bland–Altman analysis demonstrated an almost perfect concordance and agreement between single- and simultaneous dual-isotope segmental activity (123I and 99mTc). ConclusionsThis study found no impact of the acquisition mode (single vs dual) or the type of camera (DSPECT vs DNM 530c) on 123I and 99mTc defect size and mismatch, providing a new step toward simultaneous dual-isotope acquisition for combined innervation and perfusion assessment.

Simultaneous &lt;sup&gt;99m&lt;/sup&gt;tc/&lt;sup&gt;111&lt;/sup&gt;in spect reconstruction using accelerated convolution-based forced detection monte carlo

Simultaneous multi-isotope Single Photon Emission Computed Tomography (SPECT) imaging has a number of applications in cardiac, brain, and cancer imaging. The major concern however, is the significant crosstalk contamination due to photon scatter between the different isotopes. The current study focuses on a method of crosstalk compensation between two isotopes in simultaneous dual isotope SPECT acquisition applied to cancer imaging using $^{99m}$ Tc and $^{111}$ In. We have developed an iterative image reconstruction technique that simulates the photon down-scatter from one isotope into the acquisition window of a second isotope. Our approach uses an accelerated Monte Carlo (MC) technique for the forward projection step in an iterative reconstruction algorithm. The MC estimated scatter contamination of a radionuclide contained in a given projection view is then used to compensate for the photon contamination in the acquisition window of other nuclide. We use a modified ordered subset-expectation maximization (OS-EM) algorithm named simultaneous ordered subset-expectation maximization (Sim-OSEM), to perform this step. We have undertaken a number of simulation tests and phantom studies to verify this approach. The proposed reconstruction technique was also evaluated by reconstruction of experimentally acquired phantom data. Reconstruction using Sim-OSEM showed very promising results in terms of contrast recovery and uniformity of object background compared to alternative reconstruction methods implementing alternative scatter correction schemes (i.e., triple energy window or separately acquired projection data). In this study the evaluation is based on the quality of reconstructed images and activity estimated using Sim-OSEM. In order to quantitate the possible improvement in spatial resolution and signal to noise ratio (SNR) observed in this study, further simulation and experimental studies are required.

Effect of time and exercise on the clearance rate of 201Tl in normal and ischemic myocardium

Simultaneous dual isotope (SDI) acquisition of (201)Tl rest/(99m)Tc-sestamibi stress-myocardial perfusion single photon emission computed tomography is a desirable new procedure in nuclear cardiology. In this protocol (201)Tl is injected at rest but imaging is performed not earlier than after exercise. Therefore, one must be convinced that throughout exercise (201)Tl remains distributed in an identical pattern as at rest. Before SDI can be applied clinically, (201)Tl rest MPS before and after exercise test needs to be compared for equality. The aim of this study was to assess the effect of time and exercise on the clearance of preinjected (201)Tl in normal and ischemic myocardium. In 122 patients rest (201)Tl and delayed (n =20) or poststress (n= 102) (201)Tl imaging was performed. Quantitative analysis of mean counts-per-pixel was performed for each segment in a 17-segment model. Differences between rest and delayed or poststress (201)Tl MPS were calculated. Patients with a poststress (201)Tl image were divided into normal (N= 66) and ischemic (N= 36) groups. Visual analysis was performed by two independent observers scoring the 17 segments on a scale of 0-4. The overall difference between rest (201)Tl and poststress (201)Tl MPS was - 15.4%. Normal and ischemic patients showed 16.2 and 14.0% (P =0.17) washout, respectively. Visual assessment by two independent observers revealed no regional differences between rest (201)Tl and delayed or poststress (201)Tl MPS. (201)Tl poststress MPS shows significant washout of thallium. This washout is not segmental, but global over the myocardium. No significant differences are found between normal and ischemic myocardium. The poststress (201)Tl MPS is a reliable reflection of rest perfusion. SDI acquisition of (201)Tl rest/(99m)Tc-sestamibi stress-MPS is clinically applicable.

New Imaging Protocols for New Single Photon Emission CT Technologies.

Nuclear cardiology practitioners have several new technologies available with which to perform myocardial perfusion single photon emission CT (MPS). These include dedicated small-footprint cardiac scanners, new stationary or semi-stationary three-dimensional detectors, and advanced software algorithms for optimal image reconstruction. These new technologies have been employed to reduce imaging time and radiation exposure. They require less technologist and camera time and offer improved patient comfort. They have potential for the overall cost reduction of MPS and at the same time for improved accuracy by increased resolution, or accurate attenuation correction. Furthermore, these new technologies offer potential for new protocols such as simultaneous dual isotope, new combinations of isotopes, stress only MPS, or dynamic first-pass imaging. In addition, new imaging technologies in coronary CT angiography (CCTA) allow novel hybrid stress only MPS/CCTA protocols with reduced radiation burden. Additional developments further improving efficiency and diagnostic accuracy of MPS are on the horizon.

Compensation of Cross-Contamination in Simultaneous 201Tl/99mTc Myocardial Perfusion SPECT Imaging

Introduction: It is a common protocol to use 201Tl for the rest and 99mTc for the stress cardiac SPECT imaging. Theoretically, both types of imaging may be performed simultaneously using different energy windows for each radionuclide. However, a potential limitation is the cross-contamination of scattered photons from 99mTc and collimator X-rays into the 201Tl energy window. We used a middle energy window method to correct this cross-contamination. Material and Methods: Using NCAT, a typical software torso phantom was generated. An extremely thin line source of 99mTc activity was placed inside the cardiac region of the phantom and no activity in the other parts. The SimSET Monte Carlo simulator was used to image the phantom in different energy windows. To find the relationship between projections in different energy windows, deconvolution theory was used. We investigated the ability of the suggested functions in three steps: Monte Carlo simulation, phantom experiment and clinical study. In the last step, SPECT images of eleven patients who had angiographic data were acquired in different energy windows. All of these images were compared by determining the contrast between a defect or left ventricle cavity and the myocardium. Results: We found a new 2D kernel which had an exponential pattern with a much higher center. This function was used for modeling 99mTc down scatter distribution from the middle window image. X-ray distribution in the 201Tl window was also modeled as the 99mTc photopeak image convolved by a Gaussian function. Significant improvements in the contrasts of the simultaneous dual 201Tl images were found in each step before and after reconstruction. In comparison with other similar methods, better results were acquired using our suggested functions. Conclusion: Our results showed contrast improvement in thallium images after correction, however, many other parameters should be evaluated for clinical approaches. There are many advantages in simultaneous dual isotope imaging. It halves imaging time and reduces patient waiting time and discomfort. Identical rest/stress registration of images also facilitates physicists’ motion or attenuation corrections and physicians’ image interpretation.

Simultaneous 99mTC and 123I Dual-Isotope Brain Striatal Phantom Single Photon Emission Computed Tomography: Validation of 99mTC-Trodat-1 and 123I-IBZM Simultaneous Dopamine System Brain Imaging

[2[[2-[[[3-(4-chlorophenyl)-8-methyl-8-azabicyclo[3,2,1]-oct-2-yl]-methyl](2-mercaptoethyl)-amino]ethyl]amino]ethanethiolato(3-)-N2,N2',S2,S2]oxo-[1R-exo-exo)])-[99mTc]-technetium (99mTc-TRODAT-1) and 123I-iodobenzamide (123I-IBZM) are radiotracers for brain dopamine pre- and postsynaptic neuron imaging. The purpose of this study was to evaluate imaging parameters and crossed energy interference using simultaneous single photon emission computed tomography (SPECT) 99mTc and 123I data acquisition. A five-compartment brain striatal phantom was filled with 99mTc and/or 123I radioactive solutions with different striatal-to-background ratios, ranging from 3:1 to 9:1. SPECT data were acquired with energy window settings of 15% for the centered window at 140 keV for 99mTc and a 10% asymmetric window at 159 keV for 123I. The experiments were carried out using either individual (99mTc or 123I only) or both radionuclides. The striatal-to-background ratios and energy crossed interference between 99mTc and 123I were calculated. The phantom SPECT images demonstrated that the energy crossed interferences from 123I to 99mTc, and vice versa, were 22 +/- 12.4% and 0.4 +/- 1.0%, respectively. A net interference of 7.1 +/- 4.0% for the counts in the 15% centered 99mTc window can be expected from 123I and a net interference of 1.6 +/- 3.3% for the counts in the 10% asymmetric 123I window was derived from 99mTc. The correlation of striatal-to-background ratios between single isotope and simultaneous dual-isotope was excellent (R2 = 0.99). The imaging parameters used in this simultaneous dualisotope SPECT imaging could be used in future clinical practice for imaging patients with movement disorders by using 99mTc-TRODAT-1 and 123I-IBZM. The striatal-to-background ratios were not affected by the crossed interference between 99mTc and 123I.

Application of Three-Class ROC Analysis to Task-Based Image Quality Assessment of Simultaneous Dual-Isotope Myocardial Perfusion SPECT (MPS)

The diagnosis of cardiac disease using dual-isotope myocardial perfusion SPECT (MPS) is based on the defect status in both stress and rest images, and can be modeled as a three-class task of classifying patients as having no, reversible, or fixed perfusion defects. Simultaneous acquisition protocols for dual-isotope MPS imaging have gained much interest due to their advantages including perfect registration of the (201)Tl and (99m)Tc images in space and time, increased patient comfort, and higher clinical throughput. As a result of simultaneous acquisition, however, crosstalk contamination, where photons emitted by one isotope contribute to the image of the other isotope, degrades image quality. Minimizing the crosstalk is important in obtaining the best possible image quality. One way to minimize the crosstalk is to optimize the injected activity of the two isotopes by considering the three-class nature of the diagnostic problem. To effectively do so, we have previously developed a three-class receiver operating characteristic (ROC) analysis methodology that extends and unifies the decision theoretic, linear discriminant analysis, and psychophysical foundations of binary ROC analysis in a three-class paradigm. In this work, we applied the proposed three-class ROC methodology to the assessment of the image quality of simultaneous dual-isotope MPS imaging techniques and the determination of the optimal injected activity combination. In addition to this application, the rapid development of diagnostic imaging techniques has produced an increasing number of clinical diagnostic tasks that involve not only disease detection, but also disease characterization and are thus multiclass tasks. This paper provides a practical example of the application of the proposed three-class ROC analysis methodology to medical problems.

Comparison of Simultaneous Dual-Isotope Multipinhole SPECT with Rotational SPECT in a Group of Patients with Coronary Artery Disease

A triple-detector, multipinhole SPECT system was optimally configured to perform simultaneous (201)Tl (stress)/(99m)Tc (rest) myocardial perfusion imaging (MPI) using a protocol that permitted direct diagnostic comparison of this multipinhole SPECT system with conventional rotational SPECT. Both the rotational and the multipinhole SPECT systems used the same model gamma-detectors. The 2 systems were applied in tandem to study 26 patients with documented coronary status. Visual image evaluation of the MPI together with quantitative analysis using circumferential profile curves (CPC) were used for interpretation of stress/rest myocardial flow differences. A dual-peak attenuation compensation (DPAC) technique was applied to the stress (201)Tl multipinhole SPECT images by weighted combination of the images from the upper and lower peaks. Detection of myocardial infarction by location and extent correlated closely, and correlation of differential flow changes between stress and rest indicated similar accuracy in terms of location and extent of myocardial blood flow differences as well. In addition, the application of DPAC clarified the multipinhole stress (201)Tl images through reduced background and increased statistics and also improved the relative superposition of the normalized CPC, especially for the inferior and more basal reconstructed regions. The prototype 3-detector multipinhole SPECT system achieved diagnostic results comparable to those for rotational SPECT and required only a single image-acquisition session to generate stress/rest MPI and 16-segment poststress gated studies. This reduction in acquisition time significantly improves productivity without compromising diagnostic accuracy. In addition, DPAC is a useful adjunct to the multipinhole SPECT modality because it improves both the visual clarity of the stress images and the stress/rest quantitative comparability.

O-65 Simultaneous dual isotope quantification of lymphatic flow to axillary nodes from intradermal and parenchymal tissue planes compared with nodal pathology in breast carcinoma; superiority of parenchymal injection for identification of the sentinel node

O-65 Simultaneous dual isotope quantification of lymphatic flow to axillary nodes from intradermal and parenchymal tissue planes compared with nodal pathology in breast carcinoma; superiority of parenchymal injection for identification of the sentinel node

P19 Assessment of a simultaneous dual isotope lung perfusion/ventilation technique using 99mTc-MAA and 81mKr gas

Gadd, R.; Pattison, J.; Oxtoby, J.W.; Venkannagari, R.; Wheat, R.; Eustance, C.; Dainty, S.; Mountford, P.J. Author Information

Bone infection in patients suspected of complicating osteomyelitis: the diagnostic value of dual isotope bone‐granulocyte scintigraphy

The purpose of this study was to evaluate the diagnostic value of dual isotope bone-granulocyte scintigraphy in patients with known bone pathology clinically suspected of osteomyelitis, i.e. complicating osteomyelitis, using per-operative bacterial culture from bone as reference. Simultaneous dual isotope bone-granulocyte scintigraphic images were obtained in 42 consecutive patients in whom conventional X-ray, erythrocyte sedimentation rate, and C-reactive protein were also available. 99mTc MDP bone and 111In labelled granulocyte imaging was obtained simultaneously. The images were interpreted as positive for osteomyelitis if regions of interests of pathologic 111In granulocyte accumulation included 99mTc MDP activity on the bone images (except in the spine). The sensitivity, specificity, and accuracy were 84, 71 and 79%, respectively, for simultaneous, dual isotope bone-granulocyte scintigraphy, higher than the other diagnostic parameters. Simultaneous bone-granulocyte scintigraphy is a valuable diagnostic tool in diagnosing osteomyelitis complicating other bone pathology with or without soft-tissue infection.

Gamma camera PET with low energy collimators: characterization and correction of scatter

Imaging of myocardial viability with fluorodeoxyglucose (FDG) is possible with positron emission tomography (PET) and with SPECT. The image resolution from SPECT is poor but the data is reported to provide clinical information comparable to PET. Studies have just begun to appear using gamma camera PET and either axial slat collimators or open frame graded absorbers to image myocardial viability. Alternatively, it may be possible to use standard low energy collimators en detecting coincidences. Although image quality may suffer, it may be possible to devise methods such that no clinical information is lost. Such an approach also paves the way for dual isotope sequential or simultaneous imaging of coincidence and single photons. Here, we characterize the scatter fraction and scatter distribution of gamma camera PET with low energy collimators, and investigate the improvements possible with a convolution-subtraction scatter correction scheme. Monte Carlo simulations, line sources, a realistic phantom, and a human study were used. The scatter fraction was found to be almost identical to that obtained with axial slat collimators on a triple head gamma camera hybrid PET scanner. Images acquired with low energy collimators were degraded but still of good quality compared to acquisitions using axial collimation. The scatter correction scheme showed a degree of improvement over reconstructions without scatter correction. This approach is useful not only toward making sequential or simultaneous dual isotope imaging possible, but may also be useful to save time in a busy clinic that does both SPECT scans and cardiac FDG studies, since collimators would not need to be changed.

Quantitative simultaneous /sup 99m/Tc//sup 123/I SPECT: design study and validation with Monte Carlo simulations and physical acquisitions

Simultaneous dual isotope imaging (/sup 99m/Tc//sup 123/I) has potential clinical applications but has not been implemented in the clinic. The aim of this work was to design an artificial neural network (ANN) for crosstalk and scatter correction using a smaller number of energy windows (8) than we had previously proposed (26) to allow implementation on some clinical cameras, and to validate our approach using realistic Monte Carlo simulations and anthropomorphic brain phantom acquisitions. Monte Carlo simulations of dual isotope SPECT studies of a digital brain phantom and physical acquisitions of the striatal brain phantom were used to validate our approach. Corrected projections were reconstructed using an iterative ordered subsets expectation maximization (OSEM) algorithm that modeled nonuniform attenuation and variable collimator response in the projector/backprojector. Results: In Monte Carlo simulations, ANN26 and ANN8 yielded similarly accurate quantitation of /sup 123/I activity (bias <7%) in all brain structures. An asymmetric windowing method (AW) yielded accurate estimation in the striata (bias <7%) but not in other brain structures. The estimation bias of /sup 99m/Tc primary activity was <10% in all brain structures with ANN26 and ANN8.

Parameterization of Pb X-ray contamination in simultaneous Tl-201 and Tc-99m dual-isotope imaging

In simultaneous Tl-201 and Tc-99m dual isotope imaging, Pb X-rays are a significant source of contamination in the Tl image. In order to characterize this contamination, we simulated images of line sources in the Tc and Tl photopeak windows using an experimentally verified Monte Carlo program. The line sources were placed at various distances from the collimator face and emitted photons with energies from 88 to 140.5 keV. The Ph X-ray contamination line source response function in the Tl window was fitted well by a Gaussian plus an exponential function. The width of these two functions changed linearly with distance. Parameterization of the Ph X-ray response was done by simultaneously fitting the Ph X-ray response functions at various distances with fitting functions that were determined empirically to model the distance dependence of the Gaussian and exponential components of the Ph X-ray response. The parameterized model of Ph X-ray contamination is useful in developing methods to model Ph X-ray contamination in Tl-201 data by Tc-99m. This Ph X-ray contamination model can be used in iterative reconstruction-based cross-talk compensation for simultaneous Tc/Tl dual isotope imaging.